List of OTP singlespeed mountain bikes

With those eccentric BBs, is the shell bigger, or is the BB itself smaller? Presumably it's a special frame?

Also, what stops the BB holder spinning?

The shell is bigger, with an extra internal shell with a off-center, threaded hole for standard BBs to screw into. The internal shell can be rotated and lock into place to adjust tension (or infact highten/lower the BB).

I remember CharlieTheBikeMonger selling a BB which fitted standard BB shells, yet funtioned like a EBB (presumably with less adjustability). It was very expensive, but still a fantastic solution.